The benefits of MCT oil for athletes: the evidence base

The idea of using MCT oil as a “fast fat” for athletes arose back in the 1980s–1990s: if medium-chain fats are oxidized almost as fast as carbohydrates, they could become an additional fuel and preserve glycogen. The editorial team analyzed what of this was confirmed in controlled studies.

The theoretical rationale

Glycogen stores in the muscles and liver are limited, and their depletion is one of the key causes of fatigue in prolonged exertion. Fat stores, on the contrary, are enough even in lean people for many hours of work, but long-chain fats are oxidized slowly and cannot sustain high intensity.

MCT are distinguished by rapid absorption via the portal vein and entry into the mitochondria without the carnitine mechanism (Bach, Babayan, 1982). Hence the hypothesis arose: taking MCT before or during work would give muscles accessible fat, part of the energy would be obtained from it, and glycogen would be spent more slowly.

An additional argument was the ketogenicity of MCT. Ketone bodies formed in the liver from MCT could also serve as an alternative fuel for muscles and the brain.

This logic looked convincing, and in the 1990s the groups of Jeukendrup, Hawley, Noakes, and other researchers conducted a series of experiments to test it. It is precisely these works that still form the basis of the evidence base.

MCT during prolonged work

One of the first positive results was the work of Van Zyl and colleagues (1996). Cyclists, after two hours of work, performed a time trial while receiving a carbohydrate drink, an MCT drink, or their combination. The combination of carbohydrates and MCT improved the result in the final race compared with carbohydrates alone.

However, an attempt to reproduce this effect gave different results. Jeukendrup and colleagues (1998) gave cyclists a much larger amount of MCT together with carbohydrates and obtained no improvement. On the contrary, the time-trial result worsened, and the participants complained of pronounced gastrointestinal discomfort.

In the study by Goedecke and colleagues (2005) with ultra-long work, the combination of MCT with carbohydrates worsened the ability to perform sprints at the end of the distance, which the authors also linked to gastrointestinal symptoms.

The researchers see the cause of such discrepancies in the dose. The contribution of ingested MCT to energy supply is limited by how much oil the stomach can take without problems, and this amount is small. The review by Jeukendrup and Aldred (2004) concluded that at a tolerable amount the contribution of MCT to the energetics of work is too small to substantially change glycogen use or the result.

Tolerability — the main limitation

In practically all sports studies of MCT, gastrointestinal tolerability turned out to be the decisive factor. Nausea, cramps, diarrhea, and a feeling of heaviness in the abdomen intensified with increasing dose, especially during intense work.

According to estimates from reviews, without pronounced discomfort in a single intake most people tolerate only a few dozen grams of MCT, roughly up to 25–30 g. This amount is not enough to provide a significant share of energy for several hours of work.

It is important that exertion in itself reduces blood flow in the digestive tract and increases sensitivity to fats in drinks. What is comfortably tolerated at rest may cause problems during a race.

These limitations make MCT an inconvenient means for competitions. The athlete has to choose between a dose that could potentially affect energetics and a dose that will not spoil well-being.

MCT before training, body composition, and the keto diet

Taking MCT before training has also been studied. Horowitz and colleagues (2000) showed that MCT taken before work did not change the use of muscle glycogen during exertion. That is, the glycogen-sparing hypothesis was not confirmed in this scenario either.

As for body composition, the meta-analysis by Mumme and Stonehouse (2015) recorded that replacing part of the long-chain fats with MCT in the diet was associated with a small additional reduction in body weight and fat mass. For athletes who control their weight, this may be a useful supplement, but not a replacement for a calorie deficit.

For athletes on a ketogenic or low-carbohydrate diet, MCT can be a convenient energy source that eases the maintenance of ketosis. However, the ketogenic diet itself in endurance athletes is associated with reduced economy of work at high intensities, as shown by studies of the Burke group (Burke, 2021).

The review by Clegg (2010) summarized that MCT can be useful for weight control but not for increasing athletic performance. This assessment remains relevant today as well.

• Taking them before a workout does not change glycogen use.
• A small effect on body composition is possible in combination with a calorie deficit.
• On a keto diet, MCT ease the maintenance of ketosis but do not compensate for its limitations for intense work.

How to evaluate the data and who MCT might suit

Most sports studies of MCT were conducted on small groups of trained cyclists. They differed in doses, the ratio of C8 and C10, the composition of carbohydrate drinks, and test protocols. Because of this, direct comparisons are complicated, and generalizations require caution.

International recommendations on athlete nutrition (Thomas et al., 2016) do not consider MCT a means of increasing performance. The priority for endurance remains carbohydrates in sufficient quantity, adapted to the intensity and duration of the exertion.

MCT may make sense for athletes who deliberately follow a ketogenic diet, for those who find it hard to reach caloric adequacy in their diet, and also as part of a weight-control strategy. In all these cases it is a supplement to the diet, not an ergogenic additive.

If an athlete wants to try MCT, the editorial team advises starting with a small amount, combining it with food, gradually increasing the dose, and not testing the product for the first time before competitions. People with liver disease or diabetes need a doctor's consultation.

Editorial conclusions

The idea of MCT as a “fast fat” for athletes has a logical physiological basis, but in controlled studies it did not receive convincing confirmation. Isolated positive results were not reproduced, and large doses worsened performance.

The main limitation is gastrointestinal tolerability: the tolerable amount of MCT is too small to noticeably affect the energetics of prolonged work or to preserve glycogen.

MCT can be useful as part of the diet on a keto diet, for increasing caloric intake, or for weight control, but they do not replace carbohydrates as the main fuel for sport.

We also recommend reading our materials “MCT oil: what it is and how it works,” “The benefits of exogenous ketones for athletes: the evidence base,” and “Myths about exogenous ketones.”

References

1. Van Zyl CG, Lambert EV, Hawley JA, Noakes TD, Dennis SC. Effects of medium-chain triglyceride ingestion on fuel metabolism and cycling performance. J Appl Physiol. 1996;80(6):2217–2225.
2. Jeukendrup AE, Thielen JJ, Wagenmakers AJ, Brouns F, Saris WH. Effect of medium-chain triacylglycerol and carbohydrate ingestion during exercise on substrate utilization and subsequent cycling performance. Am J Clin Nutr. 1998;67(3):397–404.
3. Goedecke JH, Clark VR, Noakes TD, Lambert EV. The effects of medium-chain triacylglycerol and carbohydrate ingestion on ultra-endurance exercise performance. Int J Sport Nutr Exerc Metab. 2005;15(1):15–27.
4. Horowitz JF, Mora-Rodriguez R, Byerley LO, Coyle EF. Preexercise medium-chain triglyceride ingestion does not alter muscle glycogen use during exercise. J Appl Physiol. 2000;88(1):219–225.
5. Jeukendrup AE, Aldred S. Fat supplementation, health, and endurance performance. Nutrition. 2004;20(7–8):678–688.
6. Clegg ME. Medium-chain triglycerides are advantageous in promoting weight loss although not beneficial to exercise performance. Int J Food Sci Nutr. 2010;61(7):653–679.
7. Mumme K, Stonehouse W. Effects of medium-chain triglycerides on weight loss and body composition: a meta-analysis of randomized controlled trials. J Acad Nutr Diet. 2015;115(2):249–263.
8. Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and athletic performance. Med Sci Sports Exerc. 2016;48(3):543–568.